1. Field of the Invention
The invention relates to the field of threshold detection, and more particularly to the establishment of a threshold that is solely a function of the receiver noise level.
2. Description of the Prior Art
Received radar signals are normally converted to video signals which are then compared to a threshold level established at the output of the receiver. When the video signal exceeds the established threshold a bona fide signal detection is declared and signal processing commences. The threshold is generally set at a level that is 3 dB above the RMS value of the receiver output noise. Since the RMS value of the receiver noise may vary, a constant threshold level based on a one time measurement of the receiver noise may needlessly limit the sensitivity of the receiver at times when the noise level is low and may give rise to an excessive number of false alarms (a signal indication when no signal is in fact present) when the receiver noise exceeds the level of the noise on which the threshold is based.
Prior art detection systems average the receiver output signal and amplify this average value by 3 dB to establish the threshold signal. This is an adequate threshold when no signal is present. When a signal is present, however, a portion of the signal is averaged with the noise, increasing the threshold until feedback terminates the averaging process. Thus the signal is partially compared to itself resulting in erroneous signal parameters, such as pulse amplitude and pulse width, being reported after processing. Further, the increase in the threshold level reduces the receiver sensitivity, requiring a higher peak video signal level for detection.